Control for free-piston units



1" E Wm K. c. COOPER ,4H

CONTROL FOR FREE-PISTON UNITS Filed Jan. 30, 1945 4 SletS-Sheei; l

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:un: w, W49.. K. c. COOPER ZAMQS CONTROL FOR FREE-PISTON UNITS FiledJan. 30, 1945 4 Sheets-Sheet 2 INVENTOR Filed Jan. 30, 1945 K. C. CDQPERCONTROL FOR FREE-PISTON UNITS 4 Shee'ts-Sheet 3 Filed Jan. 30, 1945 wf QILL K. C. COOPER CONTROL FUR FREE-PISTON UNITS 4 Sheets-Sheet 4 |56 |70|54 |82 COMPRESSED GAS |NVENTORY Patented Sept. 13, 1949 UNITED STATESPATENT OFFICE CONTROL FOR FREE-PISTON UNITS Application January 30,1945, Serial No. 575,344

Claims. 1

This invention relates to a control for a freepiston unit.

. In adapting the free-piston unit to compressing media of diierentdensities as, for example, when the unit is used in aircraft; theeffective volume of the compressor has .been adjusted to compensate forthe density changes Aby providing a number of rows of spill ports in thecompressor cylinder with an arrangement for successively opening orclosing the rows of ports as a result of changes in the density of themedium. A feature of this invention is the control of the spill ports asla function of the exhaust pressure from the engine cylinder or as afunction of the scavenge pressure which is the discharge pressure of thecompressor.

In the copending Kalitinsky application, Serial No. 550,886 (Patent2,441,273), the bands which control the spill -ports are moved inresponse to a master control which indicates changes in the end positionof the piston stroke. A feature of this invention is the control of theports from the master control and also from the exhaust pressure.

lin double acting compressors the compressor cylinder may have separaterows of spill ports, one series of rows of ports controlling theelective volume of the compressor on its outward stroke and anotherseries of rows of por-ts controlling the effective volume for the inwardstroke. A feature of this invention is the control of the inner rows ofports (for the inner stroke) independently of the outer rows of portsand as a function of the scavenge or exhaust pressure of the unit.

In the copending Cooper application, Serial No. 550,876 (Patent2,426,297), the location of the inner end of the piston stroke iscontrolled by adjusting the air spring pressure. Such a controlnecessitates a source of gas under a pressure different from thepressures incidental to the operation of the unit by which to charge theair spring. A feature of this invention is a control of the location ofthe inner end of the piston stroke by adjusting the inner rows of spillports instead of by `adjusting the pressure in the -air spring.

Other objects and advantages will be apparent from the specification andclaims, and from the accompanying drawings which illustrate anembodiment of the invention.

Fig. 1 is a sectional view through the freepiston unit.

Fig. 2 is a sectional view through the synchronizing linkage.

Fig. 3 is a sectional view showing the control for one of the rows ofspill ports.

Fig. 4 is a sectional view of the master control and the valve by whichthe spill ports are controlled.

The unit shown includes an engine cylinder l0 having reciprocatingpistons I2 and I4 to which compressor pistonsll and I8 in cylinders 2|)and 22 are integrally connected. Sleeves 24 and 26 attached to thecompressor pistons complete the reciprocating piston assemblies. Thesleeves in combination with stationary pistons 28 and 30 form air springcylinders.

The piston assemblies are moved apart by the burning of fuel injectedinto engine cylinder l0 through one or more nozzles 32. Air compressedin the air spring cylinders on the power stroke returns the pistonassemblies. The assemblies are always maintained at equal distances fromthe center of the engine cylinder by a linkage which may include racks34 and 36, Fig. 2, extending from the piston assemblies and meshing witha pinion 38 on a shaft 40.

Intake manifold 42 which extends around the compressor and enginecylinders, conducts air to intake valves 44 in the heads of thecompressor cylinders through which air alternately enters opposite endsof the cylinders. The compressed air leaves the cylinders throughdischarge valves 46, also at opposite ends of the compressor cylindersand passes into a central scavenge chamber 48 and end chambers 50 and52. These chambers may be interconnected by a scavenge manifold, notshown.

Compressed gas from the scavenge chambers enters engine ports 54 and 56which are uncovered by pistons l2 and I4 at the end of the power stroke,thereby permitting air to be blown through the engine cylinder. Gas inthe engine cylinders is discharged through exhaust ports 58 into exhaustmanifold 60.

Each compressor cylinder has a number of axially spaced vents 62, eachin the form of a row of spill ports in the cylinders to permit air todischarge from the cylinder without compression. Each vent, or row ofports, may be individually controlled by a band 64, Fig. 3, extendingaround the cylinder between projecting ribs 86 extending from thecylinder, said band having spaced openings 68 for alignment with thespill ports. The band is held in place by a xed band 69 having openings10 aligned with the spill ports. The ends of this band may be connectedby a Ablock 'Il which engages over lugs 12 on the ends of the band. Theblock has gear teeth 16 engaging with a gear segment 18 on a shaft 88.The particular port closure shown is claimed in the copendlngapplication of Kalltinsksn'serial No. 550,884 (Patent 2,441,272), filedAugust 23, 1944.

The intake manifold includes a housing 82 which may extend around thecompressor cylinders, and end caps 82 and 84 on the housing formingpassages to the intake valves at the outer ends of the compressors. Thevents 82 open into the intake manifold.

In operation, assuming all the rows of ports are open and only a smallquantity of air is compressed, if the stroke lengthens, as when thedensity decreases, with Athe compressor operating at altitude, or inchanging the load, one or more of the rows of ports may be closed,beginning with the end rows, thus increasing the effective volume of thecompressor. Each row, as will be apparent, may be partially open orclosed as the control operates. 'Ihe several rows of ports permitadaptation of the compressor to substantially any altitude or to any`density of air 'being pumped, or to any load.

The rows of ports may be automatically opened and closed from the mastercontrol which produces a pressure change in a control fluid in responseto changes in an operating characteristic of the unit, such as a changein the length of piston stroke. Referring to Fig. 4, the master controlis actuated by a cam 86 turning with the pinion 38 as shwn in Fig. 2.Since the pinion 38 is oscillated directly from the pistons the movementof cam 86 is proportional to the piston stroke.

Fluid under pressure from a constant pressure source enters a passage 88in a casing 80 through a conduit`92. This passage intersects a. bore 94adjacent its outer end and a throttling screw 98 controls the rate ofilow into bore 94. A branch passage 98 from passage 88 connects with aport |00 in bore 94. A plunger |02 in bore 94 has a groove |04 whichconnects a port |08 alternately with port |00 or with a port |08. Port|06 is connectecl by a passage ||0 to the inner end of bore 94. Port|08l is connected by a channel ||2 in casing 90 and in an adjoiningcasing ||4 to the inner (left-hand) end of a bore ||8 in casing' ||4. Apiston ||8 in bore ||6 is moved to the right by a calibrated spring |20.A plunger |22 extends through the piston and carries on its projectingend a push rod |24. This rod carries a roller |28 held against cam 88 bya spring |28. Plunger |22 has a central passage |30 connecting withspaced grooves |32 and |34 in the plunger. Groove |32 aligns withopenings |36 in a sleeve |38 carried by piston I8 and groove |34 isadapted to be uncovered by the end of sleeve |38 as the plunger is movedto the right by the cam as the pistons approach the outer ends of theirstrokes.

Fluid under pressure from the right-hand end of bore 94 enters theright-hand end of bore ||8 through a connecting channel |40, movingpiston ||8 to the left against the spring |20. As plunger |22 is movedto the right by cam 86 the'groove |34 is uncovered by sleeve |38 topermit discharge of iluid from the right-hand end of bore ||6. Thepressure in the right-hand end of bore ||8 varies in accordance with thecompression of the spring and as the piston stroke becomes shorter thepiston 8 moves inward, increasing the spring tension and increasing thepressure at the end of bore 94.

Since the change in pressure on the right-hand end of plunger |02 isproportional to the change in thelocation of the end position of thepiston stroke, the pressure on the inner (left-hand) end of plunger |82which balances the pressure on the outer end must vary in the samemanner. In this way. the pressure in the discharge conduit |42 isproportional to the spacing of the actual end of the piston stroke fromthe extreme outer position of the piston, and changes in pressure inthis conduit will be proportional to changes in the outer end positionof the piston stroke. This pressure and change in pressure are used tomove the control bands for the rows of spill ports.

The outer end of the plunger |22 may reciprocate in a chamber |44 havingan outlet conduit |48 connected to a sump, not shown. The inner end ofbore ||8 may be connected by a conduit |48 to the conduit |48. A bellows|60 connected by a conduit |52 to passage |40 may be used for minimizingsurges in the controls.

The spill port control includes a casing |52 having a bore |54 in whicha plunger |58 is mounted. A port |58 is connecetd by a conduit |80 to acylinder |62 forming a part of a hydraulic motor which includes a piston|84. the cylinder is connected by a conduit |66 to a port |68 in thecasing |52. The casing also has an inlet port |10 which is alternatelyconnected to the ports |58 and |68 by the plunger |56. Plunger |58 ismoved toward the right by a spring |12,

tension of which may be adjusted by a nut |14.

A piston |16 in a bore |18 in a cap |80 on the casing engages aprojecting pin |82 on the plunger. Fluid under pressure from the innermaster control enters the end of bore |18 from conduit |42 to moveplunger |56 against the spring. Piston |16 may have a small vent |84 andthe inner end of bore |18 may be vented by a passage |08.

The piston rod |88 on piston |64has a rack |90 engaging with a pinion|92 mounted on the shaft by which the spill port band or bands areactuated. If the inner end positions of the piston stroke moves awayfrom inner dead center the fluid pressure from the master controlincreases, moving plunger |58 to the left, thereby moving piston |64 tothe right and moving the rod |90 in a direction to open the endmost rowof ports, Fig. l, that control the effective volume of the compressor onits inward stroke. If the piston stroke continues to move away frominner dead center the second and third rows of ports marked B and C inFig. 1 are successively opened. If the end of the piston stroke movestoward inner dead center the reverse occurs and the rows of ports A, Band C are successively closed in the reverse order.

The rows of ports B and C may be controlled by bands, not shown,actuated by the same mechanism above described, by means of gearsegments |94 and |86 mounted on the same shaft 80 that carries segment18. This arrangement of the gear segments angularly spaced, as shown inFig. 3, provides for the successive actuation of the bands.

In addition to controlling the spill ports as a function ofthe pistonstroke they may also be controlled as afunction of the engine exhaustpressure. To accomplish this, the exhaust duct 60 is connected by aconduit |94 to the end of casing |52 opposite to the piston |18. In thisway, when the exhaustpressure is low the pressure from the inner mastercontrol acts mainly against spring |12. As the exhaust pressureincreases, however, this pressure assists spring |12 and a greaterpressure from the inner masterl control is necessary to move plunger I58.

The outer rows of spill ports may be controlled The other end ofy by amechanism, not shown, which may be actuated by an o'uter master control.as shown, for example in the above mentioned Kalitinsky application,Serial No. 550,886 (Patent 2,441,273). By controlling the outer rows ofports (which control the effective volume of the outward stroke of thecompressor) independently of the inner rows, it will be apparent thatthe work of compression may be divided between the inner and outer endsof the compressor, thereby to obtain the desired stroke length andposition of stroke at all loads.

By control of the ports as a function of the exhaust pressure, it ispossible to maintain substantially a constant maximum pressure in theengine cylinder. This results from a change in the spill ports inresponse to changes in the exhaust pressure which has a predeterminedrelation to the scavenge pressure.

It is to be understood that the invention is not limited to the specicembodiment herein illustrated and described, but may be used in otherways without departure from its spirit as defined by the followingclaims.

I claim:

1. In a free-piston unit, a compressor cylinder, an engine cylinderhaving scavenge ports through Iwhich air under pressure from thecompressor cylinder enters the engine cylinder, an exhaust port throughwhich gas under pressure from the engine cylinder is discharged, apiston assembly in said cylinders, said compressor cylinder having anumber of axially spaced circump ferentially extending rows of spillports, and

closure members for said rows of ports, in combination with means foractuatingJr said closure members successively and a device responsive tochanges in the pressure of the exhaust gas from the engine cylinder foroperating said actuating means.

2. In a free-piston unit, a compressor cylinder, an engine cylinderhaving scavenge ports through which -air under pressure from thecompressor cylinder enters the engine cylinder, an exhaust port throughwhich gas under pressure from the engine cylinder is discharged, apiston assembly in said cylinders, said compressor cylinder having anumber of axially spaced circumferentially extending rows of spillports, and closure members for said rows of ports, in combination'withmeans for successively actuating the closure members for closing theaxially spaced ports in succession, and a device responsive to changesin the end position of the piston strokes for operating said actuatingmeans.

3. In a free-piston unit, a compressor cylinder, an engine cylinderhaving scavenge ports through which air under pressure from thecompressor cylinder enters the engine cylinder, an exhaust port throughwhich gas under pressure from the engine cylinder is discharged, apiston assembly in said cylinders, said compressor cylinder` having anumber of axially spaced circumferentially extending rows of spillports, and closure members for said rows of ports, in combination withmeans for actuating said closure members in response to changes in saidexhaust gas pressure from the engine cylinder, means responsive tomovement of the piston assembly for indicating the location of the endof the piston stroke, and means responsive to said indicating means formoving said closure members.

4. In a free-piston unit, an engine cylinder having scavenge and exhaustports, a compressor cylinder, a piston assembly in said cylinders, saidcompressor cylinder having a number of axially spaced circumferentiallyextending rows of spill ports, and closure members for each row ofports, in combination with means for actuating said closure members, adevice responsive to changes in the pressure of exhaust gas from theengine cylinder, means responsive to movement of the piston assembly forindicating the location of the ends of the piston strokes, said devicebeing responsive to said indicating means, and means operated by saiddevice for controlling said closure members.

5. In 'a free-piston unit, an engine cylinder having scavenge andexhaust ports, a compressor cylinder, a piston assembly in saidcylinders, said compressor cylinder having a number of axially spacedcircumferentially extending rows of spill ports, and closure membersforeach row of ports, in combination with means for indicating the innerend positions of the strokes of the piston assembly, and means actuatedby said indicating means and responsive to changes in the inner endpositions of the piston strokes for moving said closure members. y

6. In a free-piston unit, a compressor cylinder, an engine cylinderhaving scavenge ports through which air under pressure from thecompressor cylinder enters the engine cylinder, and exhaust portsthrough which gas under pressure from the engine cylinders isdischarged, a piston assembly movable in said cylinders, and an exhaustduct for the gas, said compressor cylinder having a number of axiallyspaced rows of spill ports, and closure members for closing the rows ofports, in combination with hydraulically actuated means for moving saidclosure members in predetermined sequence, a pressure responsive valvefor controlling the supply of uid to said hydraulic means, and aconnection from said valve to the exhaust duct for movement of the valvein response to changes in exhaust pressure.

'7. In a free-piston unit, a compressor cylinder, an engine cylinderhaving scavenge ports through which air under pressure from thecompressor cylinder enters the engine cylinder, and exhaust portsthrough which gas under pressure from the engine cylinders isdischarged, a piston assembly movable in said cylinders, and an exhaustduct for the gas, said compressor cylinder having a number of axiallyspaced rows of spill ports, and closure members for closing the rows ofports, in combination with hydraulically actuated means for moving saidclosure members in predetermined sequence, a pressure responsive valvefor controlling the supply of duid to said hydraulic means, a connectionfrom said valve to the exhaust duct for movement of the valve inresponse to changes in exhaust pressure, means for indicating changes inthe end position of the strokes of the piston assembly, and meansresponsive to said indicating means for moving said valve.

8. In a free-piston unit, a compressor cylinder, an engine cylinderhaving scavenge ports through which air under pressure from thecompressor cylinder enters the engine cylinder, and exhaust portsthrough which gas under pressure from the engine cylinders isdischarged, a piston assembly movable in said cylinders and an exhaustduct for the gas, said compressor cylinder having a number of axiallyspaced rows of spill ports, and closure members for closing the rows ofports, in combination with hydraulically actuated means for moving saidclosure members in predetermined sequence, a pressure responsive valvefor controlling the supply of fluid to said hydraulic means, and aconnection from said 9. In a free-piston unit, an engine cylinder'having scavenge and exhaust ports, a compressor cylinder, a pistonassembly in said cylinders, said compressor cylinder having a number ofaxially spaced spill ports, and closure members for each port, incombination with hydraulically actuated means for moving said closuremeans in sequence,

a pressure responsive valve for controlling the supply of nuid to saidhydraulic means, means responsive to the piston assembly movement forproducing. changes in pressure in a hydraulic circuit in response tochanges in the end position oi the strokes oi' the piston assembly, anda connection from said valve to said circuit to cause said valve to movein response to said changes in pressure.

10. In a free-piston unit, an engine cylinder having scavenge andexhaust ports, an exhaust duct connected to said ports, a compressorcylinder, a piston assembly in` said cylinders, said compressor cylinderhaving a number oi axially spaced spill ports, and closure members foreach port, in combination with hydraulically actuated means for movingsaid closure means in sequence,

a pressure responsive valve tor .controllingthe supply of nuid to saidhydraulic means, means responsive to the piston assembly movement torproducing changes in pressure in a hydraulic circuit in response tochanges in the end position oi the strokes o1 the piston assembly, aconnection from said valve to said circuit to cause said valve to movein response to said changes in pressure, and a connection from saidvalve to said exhaust duct connected to said valve such that the exhaustpressure acts on the valve in opposition to the pressure from saidchange producing means.

KENNETH C. COOPER.

REFERENCES CITED The following references are oi record in tbe ille oithis patent:

UNITED STATES PATENTS Number Name Date 877,492 Doelling Jan. 28, 19081,481,358 Dwyer Jan. 22, 1924 1,626,076 Christensen Apr. 26, 19271,642,760 Wineman Sept. 20, 1927 2,086,162 Janicke July'. 1937 2,108,890Janicke Feb. 22, 1938 2,414,744 Kalitinsky Jan. 21. 1947 2,426,297Cooper v--- Aug. 26, 1947 2,426,308 Kalitinslw Aug. 26. 1947

